The present invention relates to an image forming apparatus wherein an image signal corresponding to image information is applied to an electrode member, so that developer is directly deposited on an image bearing member, thus forming image information on the image bearing member in accordance with the image information, and to an image forming apparatus wherein the thus formed image is displayed for allowing the operator to observe the same.
As for an image forming apparatus of this type, a so-called contrography is known. In this method, an insulating film having a high electric resistance is used for a recording medium, which is moved and to which a recording electrode is closely opposed at the backside thereof. Onto the front side of the film conductive toner particles are contacted which are carried on a developing member. A recording signal voltage is applied to the recording electrode in accordance with the image information so that the toner particles are deposited on the recording medium, thus forming the image.
An example of the apparatus of this type is disclosed in Japanese Laid-Open Patent Application No. 105758/1982, which is schematically shown in FIG. 1. The recording medium made of an insulating material is movable in the direction shown by an arrow A. To the backside of the recording medium 2, the recording electrode 2 is disposed closely opposed thereto, which includes a number of needle electrodes electrically isolated from each other and arranged in the direction of the width of the recording medium. To the respective needle electrodes of the recording electrode 2, signal voltages corresponding to the image information are independently applied from a signal generator 3. A developing device 4 is disposed across the recording medium 1 from the recording electrode 2. That is, the develping device 4 is located to the frontside of the recording medium 1. The developing device 4 includes a rotatable sleeve 5 which is a hollow cylinder of non-magnetic and conductive material, and includes a stationary magnet 6 therein. The sleeve 5 is contacted to the conductive and magnetic toner particles T contained in the toner hopper 7. When the sleeve 5 rotates in the direction shown by an arrow B, the toner particles T are carried on the surface of the sleeve 5 to be brought into contact with the recording medium 1. Then, the toner particles T function as an opposite electrode of the recording electrode 2. Therefore, electric discharge takes place between the recording medium 1 and tip end of the recording electrode 2 to which the recording signal voltages are applied, whereby an electric charge appears on the recording medium 1, and simultaneously an electric charge of the opposite polarity is injected to the toner particles T from the conductive sleeve 5. The electric attraction force between those electric charges having opposite polarities retains the toner particles T on the recording medium 1, thus providing a visualized image.
However, this type of apparatus requires that a very fine clearance, several microns-several tens of microns, has to be maintained between the needle electrodes and the recording medium 1. This is very difficult to achieve uniformly over the full span of the recording medium width.
Therefore, an improvement is required in this type of apparatus.